Gas-cleaning precipitator



Aug. 9, 1960 s. w. PENNEY GAS-CLEANING PRECIPITATOR Filed Jan. 8, 1958 6 Sheets-Sheet 1 llll N\ 12 I v 0w 7 w. 265? w V/ h 3 Nu N 54 \\\\\E Aug. 9, 1960 s. w. PENNEY szxswummc PRECIPITATOR 6 Sheets-Sheet 2 Filed Jan. 8, 1958 v////////////////////lr///////////// lll/l/l/l/l/l/I/l/l Ill/\I/ll/l/ ll/I/I/l/l/I/l/ll/ Ill/Ill Ill/I'l/lI lll/llllllllllllll/l/ Fig.2

Aug. 9, 1960 s. w. PENNEY CLEANING PRECIPITATOR GAS- 6 Sheets-Sheet 3 Filed Jan. 8, 1958 Fig. 3.

Aug. 9, 1960 G. w. PENNEY 2,943,353

' GAS-CLEANING PRECIPITATOR Filed Jan. 8, 1958 6 Sheets-Sheet 4 sll Aug. 9,1960

Filed Jan. 8; 1958 G. w. PENNEY' GAS-CLEANING PRECIPITATOR 6 Sheets-Sheet .5

Aug.v9, 1960 G. w. PENNEY GAS-CLEANING PRECIPITATOR 6 Sheets-Sheet 6 Filed Jan. 8, 1958 United States Patent i 2,948,353 GAS-CLEANIN G 'PRECIPITATOR Gaylord w. Penney, 216 Louis Road, Pittsburgh 35, Pa.

My invention relates to electrical precipitators for atmospheric dust, and particularly tdtWo-Stage precipitators comprising an ionizing stage for ionizing the par"- ticles which are to be precipitated, a collector-stage for precipitating the ionized particles, and a means for causing the gas to; pass first through the ionizing stage and then through the collector-stage, as is broadly covered in my Patent No. 2,129,783, granted September 13, '1'938.

reduction in the plate-spacing Will reduce the volumetric size of the collector.

My above-mentioned patent on a two-stage gascleaning unit recommended the use of collector-plates in the form of large-area metal sheets of sufiicient thickness and stifiness to be able to stand on edge without.

excessive warping in a lateral direction, and this has been the conventional collector-construction ever since. With the collector-plates of a reasonable flatness or freedom from warping, and of a reasonable surface-area, the normal plate-spacing in commercial {two-stage gascleaning units has been from .31 to .38 inch, so as to safeguard against short-circuits between successive plates, although one manufacturer has made a collector having a plate-spacing of .19 inch, which is generally regarded as the limit, or past the limit, with the standard type of collector-cell construction. I v

My present invention involves a close-spaced collector, comprising closely spaced precipitator-plates 'which are individually so flexible as to be non-self-suppor'ting in a lateral direction, and which are held apart by a pinrality of spacer-means, preferably in the form of rows of spacer-strips, extending in the direction of ga'sdlow, and spaced laterally from each other at frequent intervals across the faces of the precipitator-pla'tesp This makes possible the use of thinner and less" expensive plates, using the term plates as meaning any thin, extensive-surface electrodes having sufficient conductivity to maintain a prescribed voltage-gradient across the precipitating spaces, said plates being either flat, cylindrical, or spiral, or of any other shape which permits the maintenance of a reasonably uniform spacing between adjacent plates.

This new type of collector-construction is adapted to quite small spacings, preferably of the order of .02 to .06 inch, or say between the limits of .015 and .08 inch.

This makes possible a considerable reduction in the size 2,948,353 Patented Aug. 9, 1960 ice . .2 to maintain a predetermined range of potential-gradients "in the precipitating spaces. It 'i'snec'es'sa'ry that these individual circuit rneans shall include su'flicien't resistances to confinethe serious deleterious operative effects of an accidental short-circuit between any two successive plates to the immediate .vici'nity of the short-circuited portion, "without imposin'gan excessive drain on the power-supply means. These provisions are necessary, because the closeness of the plate-spacings and the flexibility of. the individual recipitator plates are such as to make anaccidental short-circuit an expectable contingency which must be provided for in the design.

My novel close-spacedcollwtor-cell construction can be of either one of 'two general types, depending upon the high-resistance circuit-means which are used 'to supply the tiny plate-charging currents.

In my series-cell construction, which at present seems to be the preferred form, a plurality of cells, or precipitatingi spaces 'betweenflsu'ccessive plates, are disposed in series with each other, between two relatively widely spaced electrode-plates between which a unidirectional voltage-(inference is maintained, and, the spacers are "made of semiconductor material, so as to draw 'a leakage-curl'en't which is large, compared to the collected current which is due t'ojthe charges on the particles which are precipitated from the gas. The electrode-plates must necessarily be of a su'iilcientl'y good conductivity to have only small voltage-drops across all parts of their entire areas, but the intermediate plates are preferably of semiconductor material such as treated paper or the like, as will be subsequently explained.

My close-spaced collector may also be made in a parallel-cell construction, in which 'thefce'lls are all con "nected in parallel across a common voltage-source, the platesare all good conductor electrode-plates, and the current-limiting resistances are connected between the individual plates o'r'cells and the voltage-source.

The result of my close-spaced collector-construction is a reduction in cost, weight, and space-requirements, and other advantages which will be described hereinafter.

The essential principles of my invention will better b'e'understood from the following description of two exjernpla'r'y'forms of embodiment which are shown in the approximately 600 clim. (cubic feet per minute), in a preferred exemplary form of construction, the sect-ionplane being indicated at .II in Fig. 2, 1

Pg. 2 is a diagrammatic transverse or vertical sectional view of the same unit, as viewed from the ionizing-stage end, the section-plane being indicated at IIII in Fig. 1,

Fig. 3 shows, on a magnified scale, with parts broken away, 'a'diagrammatic transverse sectional view of one of the two series-cellcollector-units of Fig. 1, the section-plane being indicated at III-III in Fig. 1,

Fig. 4 is a reduced-scale diagrammatic front-"elevational view of a four-part metal-plate parallel-cell collectorunit, such as could be substituted for one of the two twopart series-cell collector-units of Fig. 1, as viewed from a section-plane in the position indicated approximately by the broken line A-A in Fig. 1., the reduced scale of Fig. 4.-being somewhat-larger than the reduced scale of Fig. 1., the section-plane of Fig. 4 being indicated at IV- IV in .Fig. 5-, v r

Fig. 5 is afull-scale diagrammatic transverse or vertical sectional view, with parts broken away, through a four-part metal-plate collector-unit such as is shown in Fig. 4,- the'sectioneplane being indicated atV--V in =4 and-6, and 1 Fig. '6 shows, on a magnified scale, with parts broken means for ionizingthe,dust particleswhich are to be removed frornthe air. -It i s' shown inv a familiar form 4 comprising a plurality of positively charged fine wires 5 which are stretched across the 'a'irstream' between'elongatedjgrounded' electrodes 6a, 61:}60, 6d, so that co'r'ona dust-particles.

According to my present invention, the collector-stage 4 comprises one or more of my novel close-spaced collectors, for collecting, or precipitating out,' the ionized the air-velocity through the collector-units 7 and 8., although I am not limited to this detail.

from the'fine wires will "positiyely'char'ge, or ionize, the

Y '4 over relatively large precipitating-areas which were not broken up by intermediate spacers. It now becomes possible for me to use veryithin, flimsy plates, which are cheaper, lighter in weight, and space-saving, plate for plate. Further, for my semiconducting plates, P2 to P38, P40 to P76, and the like, I can use treated paper, or other inexpensive thin sheet-material having semiconductor-properties, so that the entire collector-unit becomes so inexpensive that it may be thrown away when it becomes too dirty from an accumulation of collected dust.

When my close-spaced collector uses a plurality of cells (or precipitating spaces 9 bounded by plates), which are electrically connected in a series-circuit connection between two electrode-plates P1, P39, or P39, P77, etc., it necessary for the spacer-strips S1 to S26 to be made of semiconducting material, so that the spacer-strips will vdraw, from the electrode-plates, a 1eakage-cur rent,which is large, compared to the collected current which is car ried by the charges on, the dust-particles which are deposited on the several collector-plates; as otherwise the become inoperative or ineffective.

The general contours of the two close-spaced collec- H tor-units 7 and 8 will .be apparent from Figs. 1 and 2, while the details fof their construction are shown in a magnified representation'in Fig. 3. -each ofthe' collector-units 7 and 8 is made in two separate identical parts 7', 7" and 8f, 8", respectively, the

As shown in Fig. 1,

two parts of each. unit being serially connected, one behind the other, so that'the air passes first through one part and then through the other, as it passes through the respective collector-units. While I am 'not limited to this two-part construction, it has significant advantages in my close-spaced cell-construction, as will be subsequent- 1y. explained. f

As shown in Figs. 1 and 3, each of the parts 7', 7", 8'.and 8" of the two close-spaced collector-units 7 and 8 comprises a stack of closely spaced plates (as previously defined), each plate. being a flat sheet of ma- 'terial having a certain amount of electrical conductivity, the planes of the plates being parallel to the paths of air-flow through the respective collector-units, so that the ionized dust can be precipitated out of the air-streams as the air passes through the precipitating spaces 9 between successive plates. The particular collector-units 7 and 8 which have been chosen for illustration have a stack of two hundred twenty-nine plates, numbered from P1 to P229, in each of the four component parts 7', 7", 8' and 8". Every thirty-eighth plate, namely each of the plates P1, P39, P77, P115, P153, P191 and P229, is an electrode-plate of good-conducting material such as a metal foil or a foil-coated paper- The intermediate plates do not need to be of good electrical conductivity, and in my preferred construction they are of a semiconducting material such as a semiconducting paper which is available on the market, or ordinary paper soaked in tricresyl phosphate or other semiconducting impregnating material.

It is a characteristic feature of my invention that the collector-plates, such as P1 to P229, are closely spaced, so closely spaced that it is necessary to hold the plates apart by suitable means such as rows of'spacer-strip's S1 to S26, extending through-each of the precipitating tion which has heretofore been standard, which used relatively rigid plates which would maintain theirfspacings the necessary high resistance. design may use, for example: metal foils, or thin metal sheets about .005 or .006 inch thick, for the electrodeplates P1, P39, etc.; paper about .003 inch thickforthe 'for the spacer-strips S1 to S26. .sembling such a collector, the cardboard spacer-strips In my preferred series-cell collector-construction which is shown in Figs. 1 and 3, the spacer-strips S1 to S26 are made of cardboard which has been treated to make .it a semiconductor, or said strips may be made of semiconducting rubber, plastic, or any other materials having A preferred collectoriritermediate plates P2P38, P40P76, etc.; and cardboard may be cemented to the paper sheets and to the metal foils by some adhesive such as shellac; and the assembly may then be soaked in tricresyl phosphate, which is a fire-retardant, gives the desired degree of conductivity,

" and acts as an adhesive to hold the collected dust. Other mateiials and assembly-methods may be used, however. In practice, the blower 2 of Fig. 1 produces a blower- 'pressure such-as to cause a suit-able air-velocity of-the order of V=250 or 300 f.p.m. (feet per minute) in the precipitating spaces 9 of the collectors 7 and 8.

This velocity should not be high enough to blow the collected dust-particles off of the plate-surfaces, nor yet so low as .to make an uneconomical construction. The total facearea A of the collectors (at right angles to the air-flow),

:in square feet, will then determine the rated air-handling space depends upon the distance between the positive andnegative plates. Due to the close spacing of the plates, the total length of my collector-unit in the direction of air-flow need be only- 2 or 3 inches.

When the air-cleaning precipitator is put into operation, a suitable positive unidirectional ionizing-voltage,

;such as 13 k-v. (kilovolts), for example, is applied to the ionizing wires 5, as diagrammatically indicated in Fig. 1; and a suitable positive unidirectional precipitating-voltage, which may for convenience be the same as the ;io'niz ing voltage, is applied to tabs 10 on the alternate electrode-plates P39, P and.lP191- of. they series-cell In the course of ascollector-units '7 and 8 of Fig. '1, the number of serially connected cells being so chosen as to provide a suitable voltage-gradient of about 6,000 to 10,000 volts per inch (more or less), in the precipitating spaces 9. It is to be understood that the negative terminal of the unidirectional voltage-source is grounded, said source being diagrammatically indicated simply by the legends, +13 lcv. 'The electrode-plates P1,P77,' P153' and'P2'29 are indicated 'as'beinggrounded. r e In the air-cleaning'precipitator'shown in Figs. 1 and "2, the ionizing wires 5 of the ionizing stage 3, and the colleetor-plate's P1 to P229 ofthe two collector-units '7fand lead the ionized dust-laden air to the front edges of the entrance-faces of the two collector-units "7 and '8, respectively, at the wide ends of the V which is formed by said units, as shown in Fig. 1. The point of the V is illustrated as being closed by a vertical .guide or baffle 13, so that the air is forced to divide equally between the two collector-units 7 and 8.

The close-spacing of my collector-plates, about .04 inch in the illustrated equipment, tends to increase the air-pressure drop across the collector-units, as the air passes through the same; but this increase in pressuredrop is reduced somewhat by the considerable decrease in the collector-length L, which, in the illustrated eqiiipment, totals only about 3 inches as measured in the direction of air-flow through each of the collector-units 7 and 8. This air-pressure drop, due to air-friction in the narrow precipitating spaces 9 in the illustrated equipment, represents a pressure-drop of the order of .08 inch of water, which is not at all objectionable. In factthis much pressure-drop in the collector-units is advantageous in causing-the air to distribute itself uniformly over the entrance-faces or "face-areas of the two collector-units 7 and 8, thereby avoiding the previously experienced necessity of introducing air-bathing means for causing the air to divide evenly in all the previously used wide precipitating-spaces between the collector-plates.

The positively charged dust-particles which are collected on the negative plate-surfaces of the precipitating plates tend to charge said plates at-a rate which is dependent upon: (a) the amount of particulate matter which was originally carried by the air, (b) the average particle-diameter, and (c) the average number of electronic charges which are carried'by each dust-particle after the air has passed through the ionizing stage 3. The charge which is thus collected 'on the collector-plates, in cleaning very hazy or smoky air, maybe typically figured at something of the order of .003 microampere per c.f.m.

In the particular series-cell collectors '7 and 8 which are shown by way of illustration :in Figs. 1 to 3, the high potential-difference (13,000 volts) which is maintained between successive electrode-plates, such .as :P-1 and P39 for example, is subdivided into thirty-eight equal parts in the thirty-eight intermediate precipitating-spaces 9, :by means of twenty-six stacks of semiconducting spacerstrips S1 to S26, which are built up between these two electrode-plates, these spacers acting as otentiometers for subdividing the total voltage. As in otherpotentiometer-applications, it is necessary for these spacer-strip potentiometers to draw a leakage current which is large, say 100 times, or between 10 and 1000 times, the current which is collected by those portions of the collector- ..plate surface-areas which are to be kept at a prescribed potential by each portion of the spacer-strip potentiometers. At a leakage-current which is 100 times a maxcollector-load of, say, ,.003 microampere per c.f.m.,

or ."9 microampere per square foot of, collector facearea, said leakage-current becomes .emicroampere per its "misses -c; f.m. of collector-rating, or mrcroamperes per square foot of face-area. The leakage-power, drawn 1 by the collectors '7 and 8 otFig. '1; would then be something like .3, 10- 13 1'O ,or 5004 watt -per'c.f.m. This is to be compared to a typical ionizer-powerwhich is consumed by corona in the ionizing wires 5, which may vary between, abou'tBl and :Otvtia'tt per cl:.m., according to 'thedesign. I g

In a close-spaced paper-cell collector havingspacerstripsSlto S26 'wln ch'are fiflflhcs long, 509 inch wide, and [04 inch thick, spaced :62 "inch between center-lines or successive spacers, anacceptable resistivity of bo'th'the paper plates and "the spacer-strips will be something of the order of 3x10 or 5361 0 ohms per inch-cube.

it will he understood, of course, that the foregoing specific figures are only by way of illustration or example, as my invention is not limited toany specific figures exeept within-the rangesindicated. I

"A characteristic feature of my close-spaced 'colle'ctor design islthat the individual precipitator-plates are so flimsy or flexib'le, and they are spaced "so closely together, that an accide-nta1short-circuit between plates will be an expecta'b le contingency, which must be so provided for, in thedesi'gn, that the air-cleaning efficiency will be only minutely reduced by such a short-circuit, and that the protective high resistances which are necessarily introduced in the design "shall not result in an excessive power-consumption, either during normal fault-free op eration or during the existence of one or more shortcircuits. In my series-cell paper-plate design which has just been discussed, it has been shown that the leakagepower is quite acceptably small, and "this is true whether there is a short-circuit or not, because the successive plates can be impressedwithpnly such potentiahdiffer- 'ences as are furnished-by the semiconductor spacer-strips. As to the air-cleaning efiiciency during a short-circuit between adjacent collector-plates, the high resistivity of the semiconductor paper-plates means that if two normally spaced plates should touch at some intermediate point between two semiconductor spacer-strips, the potentialdifference between these two plates will approach zero only at the precise line of contact, or point of contact, as the case may be; because the high resistance of the plates, traversed by'the tiny short-circuit current, will produce voltage-drops which will cause the potentialdifierence to become normal in the vicinity "of the two spacer-strips, even though the potential-difference should become zero at the intermediate 'short-circuited pointor line of contact, as the case may be. Thus, a short-circuit will causeithe dust-precipitating potential gradient to be lost, or reduced, over only a very small proportion of the total dust-collecting area of the total number of collectorplates, and furthermore the air-flow will be substantially reduced at the faulted point, so that the over-all cleaning efficiency will remain high. Since, however, my close-spaced collector-unit, (unlike standard previous commercial designs), is intended to operate while there are one or more short-circuits in it, it is usually desirable, and worth the trouble, to break the total length of air-travel in each collector-unit into two half-as-long air-paths in series. Then it will be highly improbable that both half-length sections will be short-circuited for any given air-path through the collector-unit. Thus, in Fig. l, the three-inch-l'ong collector-unit 7 is divided into two separate parts 7 and 7", each 1 /2 inches long in the direction of air-flow, the part 7" being placed behind the part 7" in the direction 'of air-flow. The air-flow from the part '7 to the part 7 may "be secured by means of lateral confining-guides or batlies 14 and 15; In like manner, the unit 8 is divided into two parts, 8' and 8". This subdivision or the collector-units into a plurality of serially connected ,parts (in the direction of, air-flow) is quite ettective, because most of the air-cleaning which "is accomplished by any collector -unitis performed in the half of its length in the direction of air-flow, so that a section of half the length of the complete unit will have an air-cleaning efficiency not too much less than the whole complete unit. The close-spaced series-cell paper-plate collector-units .7 and 8 of Fig. l have the advantage of disposability, as 'well'as certain functional advantages, as have been described; but in some applications it may be a disadvantage that these paper-cell units are not normally clean- .able. Y

, In'Figs. 4 to 6, therefore, I have shown a close-spaced metal-plate collector-unit -17 which may be substituted forone of the paper-plate units 7 or 8 of Fig.1, and

'which can be cleaned with a vacuum cleaner, or by-washing with oil, or by other rnethods'.

- Instead of havingv a large number of plates in series, with their potentials determined by a limited conductivity of spacers, theuse of metal plates introduces the possibility of using spacers which are insulating, with alternate plates at ground and at a higher potential.

With close spacing between these plates inaccordance ,with my present invention, the difference in potential between adjacent plates will preferably be of the order of 300 volts, as compared to 6000 volts in wide-space units of a previously standard design. At this low potential,

it is quite feasible to feed the 300-volt plates through a strip or block of semiconductor-material.

v In the metal-plate collector-design shown in 'Figs. 4 to 6, a large number of thin, rather flimsy, metal or other good-conductor plates p1 to p229 are spaced by spacerstrips s1 to s26 in much the same manner as described for Figs. 1 to 3, except that each of the spacer-strips s1 .to :26 is an insulator which draws a negligibly small leakage-current. The metal plates p1 to p229 may all be similar to the electrode-plates P1, P39, P77, P115, P153, P191 and P229 of Figs. 1 and 3. In Figs. 4 to 6, the

odd-numbered plates, from p1 to p229, are grounded,

as by being electrically connected to a grounded wire 18, and the even-numbered plates, from p2 to p228, are connected to a positive wire or conductor 19 through highresistance connections which may advantageously be obtained by contacts between the tabs of the various plates and a semiconductor-envelope 20 which surrounds the positive wire 19. The positive wire 19 is diagrammatical- 1y illustrated as being energized from a unidirectional source of suitable voltage, such as +300 v., so as to maintain a desirable potential-gradient in the precipitat-' ing spaces 9 between successive plates such as p1 and p2, or between p2 and p3, and so on.

Assuming the same plate-spacing as in Figs. 1 to 3, the collector-unit 17 is Figs. 4 to 6 works very well (for example) with a resistance of 10 ohms per c.f.m.

handled, in series with each of the positively charged even-numbered plates, from p2 to 2228, this resistance being obtained by the semiconducting covering 20 on the wire 19. The maximum collected current in each. positive plate, when cleaning the air in a very smoky or hazy room, may be something like 4.5 X 10 amperes per plate per c.f.m. handled. Assuming this to be true, the voltage-drop through a resistance of 10 ohms, in normal operation, will be 4.5 l* lO or .45 volts,

which is quite negligible as compared to an applied potential of 300 volts.

In case of a short-circuit in the metal-plate collector, the current in the short-circuited positive plate would be 300/ 10 ampere or 3 microamperes per c.f.m. of the normal rating of-that plate, and the energy dissipated in each s P te i a sqqdedi t IFQ: this. a it i to 6 is subdivided into four parts 17a, 17b, 17a" and 17b,with the double-primed parts back of the correspondingly lettered primed parts, and with the b parts above the corresponding a parts The limits of resistance, voltage and plate-spacing, which have been given hereinabove, are for my preferred design. The most important obects of my present inven tion are to devise a small-cost, small-volume, low-power precipitator-unit of close-spacedplate-construction, which is simple to manufacture and trouble-free in service. The leakage-surfaces at the sides SS and ss of my spacers S1 to S26 and s1 to s26, in Figs. 3 and 5, are substantially normal to the-plate-surfaces, thus making a simple construction. The plate-spacing, which is determined by the thickness of the spacers, is made quite small, so that the voltage-difference between successive plates may also be made quite small because of the reduced distance which the precipitated dust-particles must travel, in the precipitating spaces between the plates. By making the platespacing less than 0.1 inch, and at the same time suitably reducing the voltage-difference between successive plates, I am enabled to use these normal leakage-surfaces SS and ss without entailing excessive surface-leakage currents such as have hampered previous attempts at a close-spaced precipitator-unit.

As essential feature of my invention is the use of resistances which will carry the small charging-currents which are necessary to maintain the requisite plate-toplate voltages in the precipitator-unit, while at the same time suitably limiting the energy which is dissipated in an accidental short-circuit between any two successive plates; thus making it practicable to use a close-spaced, flexibleplate collector in which an accidental short-circuit is an expectable contingency which must be provided for in the design. If the energy dissipated in any such short-circuit is less than 0.05 watt, or even less than 0.1 watt, these obectives can readily be obtained, involving no energydi'ssipating difficulties in order to avoid a fire-hazard or even a hot-spot. Actually, in the embodiments of my invention which have been illustrated in the accompanying drawings, the energy-loss per short-circuit is very much smaller than 0.05 watt. It might be stated, therefore, that the plate-spacing should be less than 0.1 inch, the plate-toplate voltage should be less than 1000 volts, and the energy consumed in each short-circuit should be less than 0.1 watt; or these limits could be more conservatively stated as 0.08 inch, 600 volts, and 0.05 watt, respectively. My preferred design is considerably more conservative yet.

While I have described and illustrated my invention in two different forms of embodiment, and while I have given specific exemplary possible or preferred details of the design, I wish it to be understood that my invention, in its broadest aspects, is not limited to these embodiments and these details.

I claim as my invention:

1. A two-stage gas-cleaning precipitator, comprising an ionizing stage for ionizing the particles which are to be precipitated, a collector-stage for precipitating the ionized particles, and a means for causing the gas to pass first through the ionizing stage and then through the collector-stage; said collector-stage comprising a close-spaced collector comprising a plurality of closely spaced precipitator-plates which are individually so flexible as to be non -self-supporting in a lateral direction, the space b ef! f tween said'precipitator-plates extending in direction of gas-flow; a plurality of spacer-means for holding successive precipitator-plates in closely spaced relation, said spacer-means being disposed at spaced intervals, spaced laterally of the direction of gas-flow; and a power-supply means, including individual circuit-means for the precipitating spaces between said precipitator-plates, for supplying limited amounts of current to said precipitator-plates to maintain a predetermined range of potential-gradients in said precipitating spaces, said individual circuit-means including suihcient resistances to confine the serious deleterious operative effects of anaccidental short-circuit be.- tween any two successive precipitator-plates to the immediate vicinity of the short-circuited portion, without-irnspaced collectors disposed one after another in the path of gas-flow, each collector comprising a plurality of closely spaced precipitator-plates which are individually so flexible as to be non-self-supporting in a lateral direc- I tion, the spaces betweensaid precipitator p lates extending in the direction of gas-flow; a plurality of spacer-means for holding s uccessive precipitator-plates in closely spaced relation, said spacer-means being disposed at spaced intervals, spaced laterally of the direction of gas-flow; and

a power-supply means, including individual circuit-means for the precipitating spaces between said precipitatorplates, for supplying limited amounts of current to said precipitator-plates to maintain a predetermined rangeof potential-gradients in said precipitating spaces, said individual circuit-means including sufiicient resistances to confine the serious deleterious operative effects of an accidental short-circuit between any two successive precipitator-plates to the immediate vicinity of the short-circuited portion, without imposing an excessive drain on the power-supply means; the closeness of the plate-spacings and the flexibility of the individual precipitator-plates being such as to make an accidental short-circuit an eX- pectable contingency which must be provided for in the design. v I

3. A close-spaced collector adapted for use in a twoholding successiveprecipitator-plates in closely spaced stage gas-cleaning precipitator, said collector comprising .a plurality of closely spaced precipitator-plates which are individually so flexible as to be non-self-supporting in a lateral direction, the spaces between said precipitatorplates extending in the direction of gas-flow; a pluralityof spacer-means for holding successive precipitator-plates in closely spaced relation, said spacer-means being disposed at spaced intervals,.sp-aced laterally of the direction of gas-flow; and a power-supply means, including individual circuit-means for the precipitating spaces between said precipitator-plates, for supplying limited amounts of current to said 'precipitator-pl'ates to maintain 'a predetermined range of potential-gradients in said precipitating spaces, said individual circuit-means including suflicient resistances to confine the serious deleterious operative effects of an accidental short-circuit between any two successive precipitator-plates to the immediate vicinity of the short-circuited portion, without imposing an excessive drain on the power-supply means; the close- 'ness 'of the plate-spacings and the flexibility of the individual precipitatoraplates being such as to make an acciden'tal short-circuit an expectable contingency which must be provided for in the design.

4, The invention as definedtin claim 3., characterized l0 .v by the average precipitating spacing being within the limits of 0.015 and 0.08 inch.

5. A close-spaced collector adapted for use in a twostage gas-cleaning precipitator, said collector comprising a plurality of closely spaced precipitator-plates which are individually so flexible asto be non-self-supporting in a lateral direction, the spaces between said precipitatorplates extending in the direction of gas-flow; a plurality of high r'esistance spacer-means for holding successive precipitator-plates in closely spaced relation, said spacermeans being disposed at spaced intervals, spaced laterally Of'the direction of gas-flow; and a power-supply means for maintaining a uni-directional potential-difference between two relatively widely separated plates whereby there area plurality of serially connected high-resistance spacer-strips between the plates having said potentialdifierence; the resistance of said spacer-strips being such that'the spacer-strips draw a leakage-current which is large, 'com'pared 'to the collected current which is due to the charges on the particles which are precipitated from the gas; the closeness of the plate-spacings and the flexibility of the individual precipitator-plates being such as to make an accidental short-circuit, between two successive plates fan expectable contingency which must be provided for in the design.

,6. A close-spaced collector adapted for use in a twostage gas-cleaning precipitator, said collector comprising "a pair of relatively widely separated electrode-plates of relatively good conductivity; a stack of closely spaced semi con'ducting precipitator-plates which are individually so flexible as to be non-self-supporting in a lateral direction, the spaces between said precipitator-plates extending in the direction of gas-flow, said stack of closely spaced precipitator-plates being disposed between said electrodeplates; a plurality of high-resistance spacer-means for relation, saidspa'cer-means being disposed at spaced intervals, spaced laterally of the direction of gas-flow; and

'a power-supply"means for maintaining 'a unidirectional potential-difference between said electrode-plates; the resistance of said spacer-strips being such that the spacerstrips draw a leakage-current which is large, compared "to the collected current which is due to the charges on 'precipitatorplates extending in the direction of gas-flow;

a plurality of substantially insulating spacer-means for holding successive 'precipitator-plates in closely spaced rel'at1on, said spacer-means being disposed at spaced intervals, spaced laterally of the direction of gas-flow; and

a power-supply means, including individual circuit-means for supplying limited amounts of current 'to said precipitator-plates to maintain a predetermined range of i potential-gradients between successive precipitat'or-plates, said individual circuit-means including sufiicient resistances t'o confine the serious deleterious operative effects of an accidental short-circuit between any two successive precipitator-plates to the immediate vicinity of the shortcircuited portion, without imposing an excessive drain on the power-supply means; the closeness of the platespa'cings "and the flexibility of the individual precipitatorpla'te's being such as to make an accidental short-circuit an expectable contingency which must be provided for 'in the design.

*8; A two-stage gas-cleaning precipitator, comprising an ionizing'stage forionizing the particles which are-to .;be precipitated, a collector-stage for precipitating the ionized particles, and a means for causing the gas to pass first through the ionizing stage and then through the collector-stage; said collector-stage comprising a closespaced collector comprising a plurality of closely spaced precipitator-plates which are individually so flexible as to be non-self-supporting in a lateral direction, the spaces between said precipitator-plates extending in the direc- ,tion of gas-flow; a plurality of spacer-means for holding jsdccessive precipitator-plates in closely spaced relation,

said spacer-means .being disposed at spaced intervals, spaced laterally of the direction of gas-flow; and a powersupply means, including individual circuit-means for the precipitating spaces between'said precipitator-plates, for

supplying limited amounts of current to said precipitatorplates to maintain a predetermined range of potentialgradients in said precipitating spaces, said individual circuit-means including sufi'icient resistances to confine the serious deleterious operative effects of an accidental short-circuit between any two successive precipitatorplates to the immediate vicinity of the short-circuited portion, without imposing an excessive drain on the power-supply means; the average precipitating space between two successive precipitator-plates being less than 0.1 inch, the leakage-surfaces at the sides of the spacer means being substantially normal to the plate-surfaces,

.and the range of potential-gradients in the precipitating spaces being so low that tolerably small surface-leakage currents are obtained across the spacer-means.

9. A two-stage gas-cleaning precipitator, comprising an ionizing stage for ionizing the particles which are to be precipitated, a collector-stage for precipitating the ionized particles, and a means for causing the gas to pass first through the ionizing stage and then through the collector-stage; said collector-stage comprising a plurality of close-spaced collectors disposed one after another in the path of gas-flow, each collector comprising precipitating spaces, said individual circuit-means including suflicient resistances to confine the serious deleterious operative efiects of an accidental short-circuit between any two successive precipitator-plates to the immediate vicinity ot the short-circuited portion, without imposing an excessive drain on the power-supply means; the average precipitating space between two successive precipitator-plates being less than 0.1 inch, the leakagesurfaces at the sides of the spacer-means being substantially normal to the plate-surfaces, and the range of potential-gradients in the precipitating spaces being so low that tolerably small surface-leakage currents are obtained across the spacer-means.

10. A close-spaced collector adapted for use in a twostage gas-cleaning precipitator, said collector comprising a plurality of closely spaced precipitator-plates which are individually so Flexible as to be non-self-supporting "in a lateral direction, the spaces between said precipitator-plates extending in the direction of gas-flow; a plurality of spacer-means for holding successive precipitatorplates in closely spaced relation, said spacer-means being disposed at spaced intervals, spaced laterally of the direction of gas-flow; and a power-supply means, includtain a predetermined range of -potentialsgradients in said precipitating spaces, said individual circuit-means including sufficient resistances to confine'the serious deleterious operative efiects of an accidental short-circuit'between any two successive precipitator-plates' to the immediate vicinity of the short-circuited portion, without imposing an excessive drain on the power-supply means; the average precipitating space between two successiveprecipitater-plates being less than 0.1 inch, the leakage-surfaces at the sides of the spacer-means being substantially normal to the plate-surfaces, and the range of potentialgradients in the precipitating. spaces being so low that tolerably small surface-leakage currents are obtained across the spacer-means.

11. A two-stage gas-cleaning precipitator, comprising an ionizing stage for ionizing the particles which are to be precipitated, a collector-stage for precipitating the ionized particles, and a means for causing the gas to pass first through the ionizing stage and then through the collector-stage; said collector-stage comprising a close-spaced collector comprising a plurality of closely spaced precipitator-plates which are individually so flexible as to be non-sel-f-supporting in a lateral direction, the spaces between said, precipitator-plates extending in the direction of gasfiow; a plurality of spacer-means for holding successive precipitator-plates in closely spaced relation, said spacer-means being disposed at spaced intervals, spaced laterally of the direction of gas-flow; the average precipitating space between two successive precipitator-plates being less than 0.1 inch; and a powersupply means, including individual circuit-means for the precipitating spaces between said precipitator-plates, for supplying limited amounts of current to said precipitator-plates to maintain a predetermined range of potentialdifierence of less than 1000 volts in each of the precipitating spaces, said individual circuit-means including suflicient resistances to limit the energy dissipated in an accidental short-circuit between any two successive precipitator-plates to less than 0.1 watt and to confine the serious deleterious operative effects of such a short-circuit to the immediate vicinity of the short-circuited portion.

12. A two-stage gas-cleaning precipitator, comprising an ionizing stage forionizing the particles which are to be precipitated, a collector-stage for precipitating the ionized particles, and a means for causing the gas to pass first through theionizing stage and then through the collector-stage; said collector-stage comprising a plurality of close-spaced collectors disposed one after another in the path of gas-flow, each collector comprising a plurality of closely spaced precipitator-plates which are individually so flexible as to be non-self-supporting in a lateral direction, the spaces between said precipitator-plates extending in the direction of gas-flow; a pinrality of spacer-means for holding successiveprecipitator-plates in closely spaced relation, said spacer-means being disposed at spaced intervals, spaced laterally of the direction of gas-flow; the average precipitating space between two successive precipitator-plates being less than 0.1 inch; and a power-supply means, including individual circuit-means for the precipitating spaces between said plates, for supplying limited amounts of current to said plates to maintain a predetermined range of potentialdiiference of less than 1000 volts in each of the precipitating spaces, said individual circuit-means including sutficient resistances to limit the energy dissipated in an accidental short-circuit between any two. successive precipitator-plates to less than. 0.1 watt and to confine the serious deleterious operative efiiects of such a short-circuit to the immediate vicinity of the short-circuited portion.

13. A close-spaced collector adapted for use in a twostage gas-cleaning precipitator, said collector comprising a plurality of closely spaced precipitator-plates which are individually so flexible as to be non-self-supporting in a lateral direction, the spaces between said precipitatorplates extending in the direction of gas-flow; a plurality of spacer-means for holding successive precipitator-plates in closely spaced relation, said spacer-means being disposed at spaced intervals, spaced laterally of the direction of gas-flow; the average precipitating space between two successive precipitator-plates being less than 0.1 inch; and a power-supply means, including individual circuitmeans for the precipitating spaces between said precipitator-plates, for supplying limited amounts of current to said plates to maintain a predetermined range of potential-difierence of less than 1000 volts in each of the precipitating spaces, said individual circuit-means including suflicient resistances to limit the energy dissipated in an accidental short-circuit between any two successive precipitator-plates to less than 0.1 watt and to confine the serious deleterious operative effects of such a short-circuit to the immediate vicinity of the shortcircuited portion.

14. A two-stage gas-cleaning precipitator, comprising an ionizing stage for ionizing the particles which are to be precipitated, a collector-stage for precipitating the ionized particles, and a means for causing the gas to pass first through the ionizing stage and then through the collector-stage; said collector-stage comprising a closespaced collector comprising a plurality of closely spaced precipitator-plates which are individually so flexible as to be non-self-supporting in a lateral direction, the spaces between said precipitator-plates extending in the direction of gas-flow; a plurality of spacer-means for holding successive precipitator-plates in closely spaced relation, said spacer-means being disposed at spaced intervals, spaced laterally of the direction of gas-flow; the average precipitating space between twosuccessive precipitator plates being less than 0.08 inch; and a power-supply means, including individual circuit-means for the precipitating spaces between said precipitator-pl ates, for supplying limited amounts of current to said precipitator-pl'ates to maintain a predetermined range of potential-difference of less than 600 volts in each of the precipitating spaces, said individual circuit-means including suificient resistances to limit the energy dissipated in an accidental shortcircuit between any two successive precipitator-plates to less than 0.05 Watt and to confine the serious deleterious operative effects of such a short-circuit to the immediate vicinity of the short-circuited portion.

15. A two-stage gas-cleaning precipitator, comprising an ionizing stage for ionizing the particles which are to be precipitated, a collector-stage for precipitating the ionized particles, and a means for causing the gas to pass first through the ionizing stage and then through the collector-stage; said collector-stage comprising a plucircuit-means for the precipitating spaces between said precipitator-plates, for supplying limited amounts of current to said precipitator-plates to maintain a predetermined range of potential-difl'erence of less than 600 volts in each of the precipitating spaces, said individual circuit-means including suflicient resistances to limit the energy dissipated in an accidental short-circuit between any two successive precipitator-plates to less than 0.05 watt and to confine the serious deleterious operative eflects of such a short-circuit to the immediate Vicinity of the shortcircuited portion.

16. A close-spaced collector adapted for use in a twostage gas-cleaning precipitator, said collector comprising a plurality of closely spaced precipitator-plates which are individually so flexible as to be non-self-supporting in a lateral direction, the spaces between said precip-itatorplates extending in the direction of gas-flow; a plurality of spacer-means for holding successive precipitator-plates in closely spaced relation, said spacer-means being disposed at spaced intervals, spaced laterally of the direction of gas-flow; the average precipitating space between two successive precipitator plates being less than 0.08 inch;

and a power-supply means, including individual circuitmeans for the precipitating spaces between said precipitator-plates, for supplying limited amounts of current to said precipitator-plates to maintain a predetermined range of potential-difference of less than 600 volts in each of the precipitating spaces, said individual circuit-means including suflicient resistances to limit the energy dissipated in an accidental short-circuit between any two successive precipitator-plates to less than 0.05 watt and to confine the serious deleterious operative efiects of such a short-circuit to the immediate vicinity of the shortcircuited portion.

17. A close-spaced collector adapted for use in a two-' stage gas-cleaning precipitator, said collector being a cohering mass comprising a pair of relatively widely separated electrode-plates of relatively good conductivity, a stack of closely spaced semiconducting precipitatorplates, the spaces between said p-recipitator-plates extending in the direction of gas-flow, said stack of closely spaced precipitator-plates being disposed between said electrode-plates, and a plurality of high-resistance spacerstrips, extending in the direction of gas-flow, for holding successive precipitator-plrates in closely spaced relation, said spacer-means being disposed at spaced intervals, spaced laterally of the direction of gas-flow.

References Cited in the file of this patent UNITED STATES PATENTS 1,041,421 9 Bradley Oct. 15, 1912 1,968,330 Wintermute July 31, 1934 2,359,149 Pegg Sept. 26, 1944 2,381,455 Jacob Aug. 7, 1945 2,822,057 Richardson Feb. 4, 1958 FOREIGN PATENTS 752,474- Germany Oct. 12,1952 301,258 Switzerland Aug. 31, 1954 163,097 Australia May 30, 1955 

